1. Technical Field
The present invention is directed toward electronic devices, and more particularly toward mounting and protecting microelectronic assemblies.
2. Background Art
Electronic devices, particularly portable microelectronic devices such as cellular phones, are subject to a wide variety of conditions which can interfere with proper operation of the device. For example, vibrations can cause wear at contact interfaces internal to the microelectronic device. This wear may generate contaminants, such as metal particles, that can migrate through the microelectronic device and degrade the performance of the microelectronic device. Additionally, such wear can increase the resistance of the contact interface, which also inhibits the performance of the microelectronic device. Still further, shock loads (e.g., from dropping the device) which may not be sufficient to visibly break the device can nevertheless cause the microelectronic circuitry to lose contact interfaces so as to prevent proper operation of the circuitry.
Such devices are also subjected to environmental contaminants, including moisture and dust which, if allowed to reach to the circuitry, can also interfere with its proper operation.
Thermal loads resulting from the operation of the circuitry can also cause the device and/or the microcircuitry to degrade over time. Still further, electro-magnetic impulses (EMI) or other radio frequencies (RF) in the environment can interfere with the proper operation of the microcircuitry, including particularly wireless communication devices such as cellular telephones. Such problems are common to all microelectronic assemblies using chip scale packages (CSP's) and Flip Chip packages.
Electronic circuit components have been mounted within their devices in a wide variety of manners. For example, thermally conductive gels have been used to dissipate heat from the microcircuitry of such devices.
Further, shield structures such as cans, lids, and metalized frames having electrical connection through an ohmic connection along the periphery of the shielding member have been used to provide EMI shielding and thermal control and CSP's and Flip Chip architectures. The ohmic connection is usually made with solder, conductive elastomers or compression contacts using precious metals. Thermal control has commonly been provided by conductive materials in intimate contact with the power dissipating packages which provide a low resistance path to the body of the device.
However, mounting devices such as metal cans with solder sealing for ohmic contact are difficult to assemble automatically and therefore are subject to high assembly costs and further are subject to possible uneven assembly among multiple devices. Further, if pressure contacts are used for ohmic contact for EMI shielding, high force levels are required for each contact point which can also cause problems in assembly. For example, the force required is usually greater than that which can be provided by a plastic housing without yielding the plastic, and therefore secondary fasteners or clips can be required, further increasing not only assembly costs but also costs of materials. Use of conductive elastomers require even greater force levels to maintain ohmic contact. Still further, none of these structures are entirely satisfactory for excluding moisture and dust, nor do they provide the full combination of protection of the microcircuitry from contaminants and from vibrations and shocks while also providing EMI shielding and thermal dissipation.
The present invention is directed toward overcoming one or more of the problems set forth above.